1. Field of the Invention
This invention relates to a light emitting device with a light emitting element such as an LED chip and, particularly, to a light emitting device that can prevent deterioration of a seal material and damage or deformation of LED chip due to the seal material.
Herein, an LED element is referred to as equivalent to LED chip.
2. Description of the Related Art
LED's (light emitting diodes) are characterized in low power consumption, small size, light weight, long life and low heat generation. Further, high-output blue LED's have been developed. Therefore, they are used for various applications such as electronic devices, household electrical appliances, automobiles, traffic lights, communications devices etc.
JP-A-2001-358371 discloses a light emitting device that a positive electrode and a negative electrode are disposed opposite on a base, and an LED chip is mounted on the electrodes, wherein heat generated from a light emitting layer can be directly conducted to the positive electrode through a junction material which is provided between an insulating film on a p-electrode of the LED chip and the positive electrode, so as to have a good heat radiation property (See paragraphs [0013], [0014] and [0016] and FIG. 1 thereof).
JP-A-2002-314142 discloses a light emitting device that an LED chip is mounted on a substrate and connected by wire bonding, and the LED chip is sealed with a silicone resin including a phosphor, wherein the mixed emission color of the LED chip is effected based on light absorption of the phosphor to have a constant emission property without changing color tone.
Conventionally, another light emitting device is known in which an LED chip is sealed with a resin material such as epoxy resin with low viscosity and pressure so as to prevent damage of the LED chip and deformation of bonding wires.
However, the conventional light emitting devices have problems as described below.
The light emitting device of JP-A-2001-358371 has a problem that the LED chip may be separated due to the thermal expansion of the junction material by heat generated from the LED chip.
The light emitting device of JP-A-2002-314142 has a problem that, when the silicone resin material for sealing is thermally expanded, the LED chip may be damaged or the bonding wires may be deformed.
Further, resin materials for sealing are more likely to deteriorate due to heat generated from the LED chip or light radiated therefrom according as LED chips have been developed to have higher output, shorter wavelength and larger current.